Daniel Cunningham, 39, of Ann Arbor, was charged with assaulting an individual under the age of 16, distributing a controlled substance aboard an aircraft and importing a controlled substance, U.S. Attorney Jeffrey Collins said in a statement.
The incident occurred on a flight from Amsterdam to Detroit in August. Cunningham pleaded guilty to all three counts in Federal District Court on Monday, according to the statement.
"He wanted to put this behind him," Cunningham's attorney, Neil Fink, told the Detroit Free Press for a Tuesday story.
The assault count carries a maximum penalty of one year imprisonment and a $100,000 fine. The distribution and importation charges each carry a maximum penalty of five years in prison and a $250,000 fine.
The Oakland County girl's mother, Beate Turner, took the juice off the flight after noticing that it was bitter and foamy and had blue and white specks floating in it. The girl drank some of the juice, but suffered no serious injury.
Ten days after the flight, Turner took the juice to University Laboratories in Novi, which confirmed the presence of Xanax, a prescription medication used to treat panic attacks and anxiety, the FBI has said. The drug's side effects include drowsiness, fatigue and lightheadedness.
The baby's mother and father attended Monday's hearing and said they were satisfied with the plea arrangements.
Bill Mellon, a spokesman for Northwest Airlines, had little to say about the guilty plea.
"He was let go right after the incident so there is nothing we can do," Mellon said. "We cooperated fully with the authorities. We are pleased that justice has been served."